INFLUENCE OP CERTAIN" ELEMENTS ON STEEL.
to. the determination of the other elements in both acid'and basic steel.
Another important consideration applying equally to the work on phosphorus and on manganese is the concordance of results obtained from different divisions. A general average obtained by grouping any data into two primal divisions gives conclusions of very limited value, but in this paper the practice is followed by subdividing in order to compare results. Thus from three independent lines of .Fig. XVII-B the values of phosphorus varied from 860 to 1290. It is quite possible that these variations were not accidental and that the variation represents a law of increasing effect with higher carbons; but, leaving all this aside, it is certain that three separate determinations roughly agreeing with one another establish with reasonable certainty the general fact that 0.01 per cent, of phosphorus has a strengthening effect of somewhere about 1000 Ib. The validity of the conclusions is much superior to. one based on a general average.
EFFECT OF MANGANESE ON ACID STEEL.
The heats were divided according to their content of manganese in the same way as in the determination of phosphorus. The results as given in Table XVII-Q and in Fig. XVII-C show that when the manganese exceeds 0.4 per cent, each increase in that element raises the strength, while with a content below 0.4 per cent, the tensile strength increases as the manganese decreases. The number of observations of low-manganese acid steels is not sufficient to prove this conclusively, but on another page it will be shown that in basic steel, also, a decrease in the manganese content below a certain point is not accompanied by a decrease in strength. It is probable that low manganese implies the presence of iron oxide and that this strengthens the steel much more than it is weakened by the decrease in manganese.
The lines in Fig. XVII-C show that each increase in manganese above 0.4 per cent, is accompanied by an increase in strength, but this increase is not the same with steels of different carbon. In steels containing more than 0.374 per cent, of carbon, each increase of 0.01 per cent, of manganese augments the tensile strength by about 440 Ib. per sq. in. In Table XVII-Q it is shown that the average carbon of this group is about 0.44 per cent., and we thus